Description of the Prior Art
The structure of a conventional solid-state imaging device will be described below with reference to the device shown in FIG. 5. First, a specific region of a semiconductor substrate (hereinafter abbreviated to substrate) 21 is implanted with an impurity of the same conductivity type as that of the substrate 21 to form an impurity region 22 that will isolate elements. Then, using an impurity of a different conductivity type from that of the substrate 21, a light-sensitive element region 23 and a charge transfer region 24 are separately formed in specific regions of the substrate 21. A channel region 25 implanted with a specific impurity is formed in the region of the substrate 21 between the regions 23 and 24. The structure of this channel region 25 is such that it determines the characteristics of a transistor formed by the substrate 21, regions 23 and 24, and an electrode 27a (described below).
Next, after an oxidation film 26a has been formed over the entire surface, a low-resistance polysilicon to which an impurity has been added is deposited thereon, and electrodes 27a and 27b are formed in the polysilicon by patterning. Subsequently, an insulation oxidation film 26b is formed over the top and sides of the low-resistance polysilicon by thermal oxidation.
Low-resistance polysilicon is then deposited and patterned to form electrodes 28a and 28b. After an insulating film 29 of, for instance, PSG, is formed thickly over the entire surface by a vapor growth method, a light-proof film consisting of aluminum is deposited thereon. Part of the light-proof film corresponding to the light-sensitive element region 23 is removed by patterning, exposing a hole portion corresponding to the light-sensitive element region 23 while leaving light-proof films 30a and 30b on the insulating film 29, covering the regions outside the portion corresponding to the light-sensitive element region 23.
In the solid-state imaging device constructed as described above, electric charge due to light incident on the hole portion defined by the light-proof films 30a and 30b is accumulated in the light-sensitive element formed by the substrate 21 and the light-sensitive element region 23. The transistor formed by the regions 23 and 24 and the electrode 27a operates so that the charge accumulated in the light-sensitive element is read out by the electrode 27a in the charge transfer region 24. A voltage differential is created between the electrodes 27a, 28a, 27b, and 28b, transferring the charge in sequence from right to left (as seen in the figure) within the charge transfer region 24.